This invention relates generally to patterned organic crystals and in particular to organic crystals adapted for use in electro-optic modulators and the method for patterning the relatively soft organic crystal to obtain a desired pattern having relatively smooth surfaces adapted for optically coupling light between the organic crystal and an adjoining medium.
Electro-optic modulators are devices which selectively pass light of a particular polarization in response to an applied electric field. Control of the applied electric field thus provides a means of modulating an optical signal. Optical processing of information typically offers advantages over electronic-only processing in that optical processing systems can provide faster processing, take up less space and weight, and are less susceptible to interference from environmental conditions (such as electromagnetic interference). For example, optical processing systems incorporating electro-optic modulators can be used in signal processing systems in satellites to reduce weight (and therefore launch costs) and susceptibility to electromagnetic interference; in medical equipment such as ultrasound devices to save space and allow increased density of imaging pixels; as electric field sensors in sensitive areas, such as where high radiation fields exist (e.g., in some medical imaging devices); and in phased array radar systems in which the optical processing provides high data rates along with the space, weight, and stability advantages.
Inorganic crystals such as lithium niobate or lithium tantalate are commonly used as electro-optic modulators. One measure of a material's sensitivity as an electro-optic material is the electro-optic figure of merit (FOM), which is determined in accordance with the following formula: EQU FOM=n.sup.3 r/.epsilon.
in which n is the refractive index; PA1 r is the Pockels coefficient; and PA1 .epsilon. is the dielectric constant at the sampling frequencies of interest.
Lithium niobate, for example, has a FOM of 11.4 pm/V, and lithium tantalate has a FOM of 7.1 pm/V.
In qualitative terms, an effective electro-optic modulator desirably is capable of rapidly modulating an optical signal, thus allowing a high data rate for information passed by the optical signal. The modulating material preferably is thermally and mechanically stable and further comprises a material that can be readily patterned to form smooth surfaces which are appropriate for coupling light between an adjoining medium and the modulator material. It is further desirable that the modulator material be readily patterned into structures that are adapted for use as modulators, providing, for example, for placement of electrodes on the modulator device and attachment of the device to substrates to allow coupling to other optical components. A further desirable characteristic of a modulator is the ability to be driven by a relatively low voltage (electric field).
It is thus an object of this invention to provide a high performance electro-optic modulator that provides high speed modulation capability with high damage thresholds (e.g., as shown by high mechanical and thermal stability), low drive voltages, and optical transparency in a useful window.
A further object of this invention is to provide a method of readily patterning an organic crystal material having the desired electro-optic modulator characteristics.
A still further object of this invention is to provide a non-contact, self-developing precision patterning method for a soft organic crystal.
Another object of this invention is to provide a precision patterning method for organic crystals that reduces damage to the substrate material underlying the crystal.
A yet further object of this invention is to provide a precision patterning method that can be used for making structures having a relatively high aspect ratio in a soft organic crystal.